Optimizing Nanofluidic Energy Harvesting in Synthetic Clay‐based Membranes by Annealing Treatment

Abstract Nanofluidic energy harvesting from salinity gradients is studied in 2D nanomaterials‐based membranes with promising performance as high ion selectivity and fast ion transport. In addition, moving forward to scalable, feasible systems requires environmentally friendly materials to make the application sustainable. Clay‐based membranes are attractive for being environmentally friendly, non‐hazardous, and easy to manipulate materials. However, achieving underwater stability for clay‐based membranes remains challenging. In this work, the synthetic clay Laponite is used to prepare clay‐based membranes with high stability and excellent performance for osmotic energy harvesting. The Laponite membranes (Lap‐membranes) are stabilized by low‐temperature annealing treatment to effectively reduce the interlayer space, achieving a continuous operation under salinity gradients. Furthermore, the Lap‐membranes conserve integrity while soaking in water for more than one month. The output power density improves from ≈4.97 W m−2 on the pristine membrane to ≈9.89 W m−2 in the membrane treated 12 h at 300 °C from a 30‐fold concentration gradient. Especially, It is found that the presence of interlayer water to be favorable for ion transport. Different mechanisms are proposed in the Lap‐membranes involved for efficient ion selectivity and the states found with varying annealing temperatures. This work demonstrates the potential application of Laponite based nanomaterials for nanofluidic energy harvesting.


Figure S5 .
Figure S5.Water contact angle for a reassembled Lap-membrane displaying the high hydrophilic property of the membrane.

Figure S6 .
Figure S6.Water stability test for pristine Lap-membrane in DI water.At 30 minutes the membrane is fully hydrated, and it starts delaminating in less than 2 hours.*Note: membranes have been digitally coloured for clarity.

Figure S10 .
Figure S10.(a)XRD of a Lap-membrane before and after TGA.Amorphous structure changes to Enstatite MgSiO3 (ENS) and Forsterite Mg2SiO4 (FOR) phases after 650°C.[2] (b) the phase change was accompanied by a change in colour and texture in the membranes.

Figure S12 .
Figure S12.XRD of Lap-membranes.Number indicates the temperature of annealing treatment in °C.

Figure S13 .
Figure S13.Water stability in DI water for the different Lap-membranes.

Figure S18 .
Figure S18.(a) Output power density and (b) output current density of the Lapmembranes with different nanosheet contents as functions of load resistance.

Figure S19 .
Figure S19.(a)-(c) Current density, membrane potential, maximum power density and cation transfer number under hyper salinity and artificial sea water concentration gradients 500-fold and 50-fold (CH/CL, CL fixed to 10mᴍ) for the thermally treated membranes at 300°C (mean ± SD, n = 3).(d) Output current density and output power density as function of load resistance at the 50-fold.

Table S1 .
Mass loss analysis per zone.

Table S2 .
Output power density and efficiency of representative membranes in the literature.